Microphonic transmitter



G. B. FRENCH MICROPHONIG TMNSMIT'LTR Filed April 12 1926 Patented Oct.8, 1929 UNITED s'iAir-:s

ser

GEORGE B. FRENCH, OF SOUTHAMPTON, NEW YORK, ASSGNOR TO FRENCH ELECTRICCO., INCORPORATED, 0F NEW YGRK, N. Y., A CORPORATON OF NEVI YORKMICRGPIEONIC TRANSMITTER Application filed April 12,

My invention relates more particularly to an improved method andapparatus'for accurately transmitting sound Waves or Waves adapted forthe reproduction of sound Waves in an electro-magnetic receivinginstrument. In other Words, my improvement relates to the employment Vofmeans capable of cooperation with a microphonic element in thetransmission of sound Waves of pure tone and adapted to be reproducedmore clearly and accurately than has been possible by the ordinarytransmitting and receivine apparatus heretofore in use.

Heretofore itfhas been common practice,

,both in the transmitter and receiver, to use a diaphragm having asmooth surface, With relatively high reflecting qualities, and capableof considerable amplitude of mechanical vibration. Such a diaphragm isusually fas- ;tened at its periphery and, in the case of thetransmitter, is adapted to be vibrated in response to the mechanical airpressures of ysound Waves impinging on the diaphragm.

In the case of the receiver, the diaphragm is adapted to respond to thevarying pull of a magnet controlled by an electric circuit of variablestrength.

In the ordinary microphonic transmitter, the diaphragm is adapted tovibrate with considerable, though Varying,l amplitude when sound Wavesenter the mouthpiece of the transmitter, and these vibrations of thediaphragm are adaptedto vary the pressure upon the contacts betweencarbon particles Yor granules of the microphonic element, and thereby tovary resistance to a current passing therethrough. Flow of the current,therefore, will correspond more or less to the movements or vibrationsof the diaphragm, which correspond in general to the sound Wavesstriking the latter.

These variable currents of the microphonic element upon passing throughva -coil suirounding the magnet in the receiver, will cause' thediaphragm of the receiver to vibrate magnetically, according to thevariations inthe strength of the current and thereby reproducevibrations corresponding to the original sound vibrations impresseduponthe dia-` phragm of the transmitter.k

. duction.

1926. Serial No. 101,258.

It has been customary in priordevices to use diaphragrns, in both thetransmitter and the ieceiver,",vhich have a considerable range ofvibratory movement and also since *thel surfaces of the diaphragme usedare usually hard and highly polished, the respective diaphragme arecapable of considerable reflective action on sound Waves receivedthereby.

rlhis reflective character of the usual diaphragm, it has been found,Will result in considerable.l interference With the incoming theinicrophonic element are not iny accord With' the primary or originalsound Waves it is desired to transmit. `As a result, these distortionsand interferences prevent a pure tone.

reproduction of the sound Waves impinging upon the moving and reflectingtransmitter diaphragm. Consequently, the vibrations produced by thediaphragm upon the carbon microphone are not exact reproductions of theoriginal sound Waves.` There is still a further ldistortion due to thenatural periodicity ofthe diaphragm. F or instance, in the type vofdiaphragm novv in use there is a marked distortion of sound reproduced,due to the fact that the transmitting and receiving' diaphi'agnes,Awhich have their peripheries fixed,

have a variable amplitude of vibration from the center to theperipheryand these varying amplitudes affect the purity-of tonerepronated, and receptionmaterially improved, by using a diaphragmor a'solid fdisc orblock sound Waves are preferably transmitted by moleculary Wave' motions v.vant-hin the material or the diaphragm.

These various objections anddefects of the ordinary transmitter mayAbe-rey duced to a vminimum or substantially elimi-A Therefore, inovercoming these objections, my invention contemplates the use of adiaphragm, disc or block, forming the transmitting element, ofrelatively soft or soundabsorbing material, such as Wood, cork or thelike, and of sufficient thiclrness to prevent any appreciable amplitudekof vibration thereof, as a Whole, in response to impinging sound Waves.Furthermore, my improvement contemplates minimizing or, to an extentsufficient for practical purposes, eliminating the reflection of soundWaves from the surface of the transmitting element, diaphragm or medium.Furthermore, the material used and the relative disposition thereof, asto the microphonic element, is arranged so as to give the diaphragm ortransmitting velement a minimum amplitude of vibration and, therefore, anaturalV periadicity of low frequency. i

The primary object therefore, of my improvement is to provide a solidtransmitting medium adapted to receive and absorb sound Waves and thencetransmit them, by molecular vibrations Within the material, to amicrophonic element, the latter being` so arranged that variation of theresistance is effected by the pressure of the transmitted molecularWaves, whereby the current in a receiving instrument is controlled torepro Y duce the sounds.

A further object is to provide a solid transmitting medium or element ofthis character with an absorbing or non-reflecting surface for receivingthe sound Waves to be transmitted therethrough by molecular Waves to themicrophonic element.

InV carrying out these objects in my improved transmitter, it is foundthat the objectionable characteristics, hereinbefore Vreferred to, aresubstantially eliminated and, since the sound Waves entering thetransmitter are transmitted thro ugh a solid medium by molecularvibrations adapted to produce Waves exerting pressure upon the variableresistance of the microphonic element, the fundamental tones andover-tones or partials transmitted are clearer and purer and lesssubject to Vdistortion than those trans- `mitted by the ordinarydiaphragm transmitter. As a result of transmitting sounds by my method,it Will be understood that the diaphragm of a receiving instrument inconnection therewith, will emit sound Waves which are clearer and ofmuch greater purity of tone, but of less volume, unless amplified ashereinafter pointed out. For this reason, it will be understood that, onaccount of the pure tones transmitted, the amount of ampliicationWithout distortion may be very much greater, and therefore, my'Vimprovement is particularly adaptable for the use of the deaf, forordinary telephone lbroadcasting, for radio. broadcasting, for makingtalking-machine records and for other uses rea-r face thereof, formed byan annular flange Where correct and articulate reproduction of soundWaves is the desideratum, simply by the insertion of suitable amplifyingmeans between the transmitter and the receiver.

ln the accompanying drawings, I have illustrated several forms andadaptations for carrying out my improvement, together with amplifyingcircuits, adapted to include a form of my improved transmitter. Fig. lshows one form of my improved transmitter, in which the diaphragm ismade up of a thick disc of relatively soft material, such as Wood orcork; Fig. 2 is a side elevation of a modification, which may besubstituted for the ordinary telephone transmitter; Fig. 3 is ahorizontal section of the form shown in Fig. 2; Fig. l is a Wiringdiagram, showing the arrangement as applied yto the ordinary poelretphone for the deaf, and Fig. 5 is a wiring diagram illustratingamplification of the transmitted sounds by the use of radio tubecircuits.

Referring more particularly to the form shown in Fig. l, it Will beseen' that my improvement is applied to the ordinary type of microphoneti" ismitter, wherein the casing l is preferably provided With acylindrical elongation f to provide for mounting therein a disc 3 ofwood, corlr or other suitable material, of a character to absorb andthen to transmit the sound waves by molecular vibrations of thematerial. lt Will be seen that the diaphragm or disc 3 is preferablymade of sufficient thichness to practically eliminate vibrations of thediaphragm as a Whole. ln the present instance, the disc 3 is shown as`held in place by the front section 4 of the casing, Which is preferablyspaced away from surface of the disc to form a compression chamber 5,substantially as shown in Fig. l. The usual mouthpiece 6 is screwed intoa bushing 7, surrounding the perforations S in the front casing a, sothat air sound Waves entering the mouth piece may be impressed upon thefront face of the disc or diaphragm 3. The front face 9 of the disc 3 ispreferably unpolished or even roughen'ed, so as to reduce thereflet-ting surface to a minimum. lf desired, the disc 3 may berelatively thin and have its front surface coated Wit-h a suitable soundabsorbing material. Obviously, if the disc 3 is made of cork or softWood,

or roughened material, the natural surface of the material receiving thesound Waves Will beless likely t-o reflect them and hence absorption andmolecular transmission thereby Will be more readily effected.

En the present instance, the disc 3 is preferably provided with apoclret or bore in the l0, in Which the n'ilcrophonic elementis in-Vserted., This latter preferably comprises a small cup-like container llin the bottom of which there is located one of the carbon discs 12. Ontop of the carbon dise l2, there is packed a quantity of carbonparticles or granules 13, which are preferably packed solid and a.second carbon disc 14 is placed on top or" the carbon granules 13. Thecarbon disc le engages the bottom of the pocket formed by the annularflange 10 on the rear face of the disc 3, as Will be seen in Fig. l ofthe drawings. A lead Wire 15 may be connected With the inner carbon disc111- and another lead wire 1G connected with the outer cui-bon disc 12for completing the circuit to the receiver in the usual manner. Themicrophonic element ifi-L1- is arranged to lit closely between the rearface of the disc 3 and the wall of the rear casing 1, so that when soundwaves as inolegular vibrations of .the solid material of the disc aretransmitted therethrough to the carbon disc 14, the Waves thustransn'iitted will vary the pressure on the :arbon particles 13 andthereby vary the current flowing to the receiver, Which is adapted toreproduce the sounds, as previouslypointed out.

In the form of my iii'ipi'oveinent'shown in Fig. 2, instead of a disc ordiaphragm, of Wood, corlr or similar material, adapted for thetransmission of sound ivaves by molecular vibrations, I have substituteda block of Wood 17, which is provided with a pocket 18 in which themicrophonic element is mounted. In this form, the carbon discs 19 and 2Oare provided ivi-th s-"reiv threaded tcrn'iinals 21 and 22 to which therespective leads 23 and 24 may be secured for completing the circuit tothe receiver in the usual manner. lVithin the pocket 1S and between thecarbon discs 19 and 20, there is packed a quantity of carbon )articles25 sufficient to comnletel and tightly lill the pocket and the spacebetween the carbon discs, so that any vibrations Within the solidmaterial of the Wood block will be transmitted to the carbon particlesto vary the resistance in the mass thereof between the carbon discs,thereby varying the flow of current adapted for reproducing the Waves inthe ieceiver. In this form of my improvement, the mout-li piece 26 ispreferably formed of soft material, capable of absorbing sound Waves,such as cork or the like.

As previously pointed out, my improved microphonic transmit-ter isparticularly adapted for use in phones for the deaf and a circuit forthe usual pocket set is shown in the diagram of Fig. i1f. improvedtransmitter, substantially as shown in Fig. 1, is represented at 2?, asconnected in circuit with a battery, 28., the circuit being completedthrough the primary 29, of an induction coil, the secondary SOof theinduction f coil is connected b v lea-ds 31 with ear phones 32, whichmay be of the usual or any preferred construction. fith this form ofcircuit, the vibrations transmitted by my improved microphonictransmitter are amplified by the induction coil 29--30, and reproducedby the In this diagram, myV

receiver 32 inclear, puretones, for as pre-f viously pointed out, thesound Waves ieach-` Y ing my improved transmitter are transmittedthrough the discv 3 as molecularvib 1ations or Waves ofpure tones whichmaybe,amplified` enormously Without distortiomthe latter being 'anessential requirement' for a deaf phone. Furthermore, my improvedtransmitter eliminates'extraneous sounds, which in the ordinary deafphone, produces a continuous hum ming ory crackling noise.

In F ig. 5, I have shown a Wiring diagram,

wherein amplification is effected by radio tubes and circuits,corresponding substan- Y tially to audio amplification inthe ordinaryradio receiving set. In this diagram, my improved transmitterisrepresented yat 33, and is placed in the primary circuit 34 of aninduction-coil, the secondary 35 of which is connected vwith the grid ofa radio tube 36. The plateof theiradio tube36 is connected with theprimary 37, of a second induction coil, thefsecondary 38'of which 'isconnected fr with the grid of a second radio tube 39, the plate of whichis connectedto the ear phones 4:0, substantially as indicated in Fig. 5.lVith radio tube amplification', as just described, it

has been found that the pure tones delivered or transmitted by myimproved transmitter vdeparting from the spirit and scope of theinvent-ion.

I claimt- 1.r A microphonic transmitterfcomprising a block of solidmaterial uponwhich sound Waves may be impressed, the block of materialbeing adapted to absorb sound vvaves and transmit them as molecularvibrations Within and through the'material, a mass of closely packedfinely divided microphonicV material arranged to receive said molecularv vibrations and transform them into variable electric currents foroperating a receiver, substantially as described.

2. A microplioiiic transmitter comprising a block of` solid materialupon Which sound Waves may be impressed and transformed into molecularvibrations Within the materialand closely paclrediinely divided micro*phonic material adapted to receive said molecular vibrations andtransform them into ioo isc

specified.

variable electric currents for operating -a receiver, substantally'asdescribed.

3. A mierophonie transmitter comprising a solid block of materialadapted for trans- Vmi ting sound Waves impressed thereon by molecularVibrations Within the material, the sound receiving face of saidtransmitting block or material being arranged and adapted to absorbsound Waves, and a. mierophonie variable resistance conductor of solidlypacked finely divided material mounted in cooperative relation with saidsolid transmitting block of material7 whereby said molecular vibrationsset up therein are adapted to `vary the resistance in the mierophoniematerial and thereby Vary the eleetriecurrent passing therethrough, fortheV purpose specified. f

' 4. A transmitter for sound Waves compris- ;ing a bloc-kof solid'material adapted to transmit sound Waves impressed thereon by trans`forming them into molecular vibrations Within the material andtransmitting them therethrough, and means associated With said lbloelrwhereby said molecular vibrations Within the material thereof areadapted to Vary the resistance in a mass of solidly packed mierophoniematerial and thereby transmit Variable electric currents for the purposeGEORGE E. FRENCH.

